Isn't the salary fixation in the Middle East based on Nationality instead of merit?

While the nationality does (unfortunately) play some role, it would be a gross generalization to say that companies don't try to assess merit or that they don't compensate meric.
Examples are abound in Gulf and other Arab countries of people of all nationalities in top positions who earn top dollars.
It's also useful to look at it from this logical angle: It would be more likely to see people from developing countries accept low-pay jobs because those professionals may still be better off when they compare to home opportunities.
This is not the case for professionals from rich Western countries who wouldn't be justified to settle for low pay jobs in Arab countries since they have a higher reference point.
This doesn't mean that those Westerners are favoured for high pay jobs - it only means that those are the only jobs they would be interested in applying for.

yes

In the UAE and in other countries (Qatar for example) the local companies have to hire foreigners to develop themselves.
And those foreigners need a good proposition to leave there home country.

Unfortunately ,yes it is!

It is based on active "Citizenship" as nationality is an entirely different thing. You can be a national of India, but you can still hold citizenship in the U.K and living residence in the U.K and thus have a salary conditional on the U.K citizenship. The reason for the salary fixation is based on the possibilities that are afforded to citizens of countries where the living expenses are higher AND the possibilities of greater pay are also higher.

 

Yes there is no denying this fact.

Unfortunately yes.